(P2) Cytotoxic lymphocyte protease granzyme M is differentially expressed in PBMCs of Elite Controllers and targets HIV-1 Gag
Robert van Domselaar, Pol Figueras Ivern, Niels Bovenschen, Ujjwal Neogi, Anders Sönnerborg[1,3]
 Division of Infectious Diseases and Dermatology, ANA Futura Laboratory, Department of Medicine Huddinge, Karolinska Institutet, Stockholm, Sweden  Department of Pathology and Laboratory of Translational Immunology, University Medical Center Utrecht, The Netherlands[  Division of Clinical Microbiology, ANA Futura Laboratory, Department of Laboratory Medicine, Karolinska Institutet, Stockholm, Sweden
Background: HIV-1 will lead to progression to AIDS and death of infected individuals who do not receive successful antiretroviral therapy. However, a very small group of individuals are able to control their infection naturally. How these so-called “Elite Controllers” (EC) achieve this natural suppression remains unclear. In this study, we examined differences in expression of the cytotoxic lymphocyte protease granzyme M (GrM) among HIV-1 patient groups and its antiviral function towards HIV-1 Gag.
Methods: We performed transcriptomic and proteomic analysis to assess differences in expression levels of GrM within peripheral blood mononuclear cells (PBMCs) of untreated HIV-1-infected individuals with immunodeficiency, viral progressors (VP), and EC. Since the HIV-1 Gag protein contains a putative GrM cleavage site in its P6 late domain, we tested whether GrM can target the Gag protein. For this, we overexpressed various Gag variants in cells, including subtypes B and C with or without the tetrapeptide insertion PYKE (Gag-PYKE), incubated their lysates with GrM and performed immunoblot analysis.
Results: Transcriptomic analysis on PBMCs from HIV-1-infected patient groups revealed that expression of the cytotoxic lymphocyte protease granzyme M (GrM) is increased in EC compared to VP. Proteomics analysis showed an opposite expression pattern for GrM with the highest protein expression in VP. Immunoblot analysis showed that GrM was able to cleave various variants of the Gag protein of which the Gag-PYKE variant was cleaved with extreme high efficiency.
Conclusions: We showed that GrM expression levels differ between EC and VP and that GrM can target the HIV-1 Gag protein. The increased efficiency of GrM to cleave Gag-PYKE could be an indication that host immunity directs the evolution of HIV-1 subtypes. Furthermore, these data could hint towards an immunological mechanism by which GrM-positive cytotoxic lymphocytes target the HIV-1 Gag protein within infected cells in order to control HIV-1 infection. This mechanism could be exploited in new therapeutic strategies to treat HIV-1-infected patients to convert them to EC.